PROFILE

Physics student delves into ‘skin effect’ on plasma

By Amie Lynn Shirkie

PhD student Yuriy Tyshetskiy is going on to further studies.

Photo by Amie Lynn Shirkie

Sometimes, a little encouragement can go a long way.

U of S doctoral student Yuriy Tyshetskiy says he was never very successful in his high school physics class until his teacher urged him to participate in the Physics Olympics. The event, which “required creative thinking and proposed some very interesting problems,” got Tyshetskiy interested in physics, and the support he received from his peers helped him to believe in his abilities.

Now, as Tyshetskiy completes his PhD in physics, the extent of his abilities is clear: His research has not only led to a better understanding of important physical phenomena, it will also serve as a springboard for further study.

Tyshetskiy studied at the physics and technology department of Kharkiv State University, “one of the leading institutions in the world in the study of physics,” before coming to the U of S to begin his doctoral studies in 2000. Tyshetskiy says he was interested in studying at the U of S because he wanted to work with Prof. Andrei Smolyakov, “a very good theorist, well known in his field.”

Under Smolyakov’s supervision, Tyshetskiy studied non-linear effects and heating in gas discharge plasma in the regime of anomalous skin effect. Plasma, explains Tyshetskiy, is an ionized gas. Due to the interaction of charged particles, plasma is subject to a huge amount of phenomena, making it a much more complex media than simple gas. Tyshetskiy focused on radio-frequency gas discharge plasma, which is used in applications like material processing and mass spectrometry.

Skin effect refers to the interaction of the electromagnetic field with such plasma. “It’s called skin effect because in low frequency, electromagnetic waves only penetrate into a very thin region of the plasma.”

According to Tyshetskiy, the temperature of the electrons in the plasma plays a significant factor in the interaction of plasma with the electromagnetic field. Classical skin effect, says Tyshetskiy, “describes the penetration of the electromagnetic field into plasma with cold electrons, and anomalous skin effect describes the same penetration into plasma with so-called ‘warm’ electrons.” The interaction between warm plasma and the electromagnetic field is far more complicated than that of classical skin effect.

Tyshetskiy was interested in discovering the answers to two questions: how the electromagnetic field heats plasma, and what force the field exerts onto the plasma. Explaining how plasma is heated by the electromagnetic field, Tyshetskiy explains, “It’s like when light heats a mirror. Most of the light bounces off the mirror, but some will also penetrate to a very thin depth into the foil of the mirror. Because of this, the light introduces some pressure onto the mirror, analogous to what happens when an electromagnetic wave hits plasma. Also, because it penetrates a little into the mirror, the light introduces a fraction of its energy into the mirror material and heats the mirror up.”

The challenge, according to Tyshetskiy, was to develop a model that would account for thermal motion of the electrons, in order to correctly describe these phenomena. “What we developed was a simple kinetic theory describing the response of plasma to the electromagnetic wave for the case of warm electrons, and we were able to derive relatively simple expressions for the plasma heating and force due to electromagnetic waves.” Tyshetskiy then compared his theory to some experimental results, and found that his model agreed very well with the experimental data. “This model was able to explain some surprising experimental results of measuring the non-linear force exerted onto plasma by electromagnetic waves,” says Tyshetskiy. This model also allowed him to predict new effects that had not been reported previously.

To further verify his theoretical predictions, Tyshetskiy also conducted numerical computer simulations. Together with Frank Detering, a fellow Physics graduate student, Tyshetskiy built two Linux clusters, small super computers able to perform several tasks simultaneously. They nicknamed one cluster Sasquatch, and the other Caesar, after Julius Caesar, “because he reportedly could do several things at one time.” The results of the computer simulations run on these clusters confirmed Tyshetskiy’s theoretical predictions.

Tyshetskiy believes his findings will be of use to the physics community and will provide a basis for further theoretical and experimental research. Describing the benefits of his study, Tyshetskiy asserts, “We now have a better understanding of the basic phenomena of the skin effect regime, and we have been able to explain experimental effects. These results can be used for building new models of low frequency gas discharges.”

Tyshetskiy says he would like to continue to study plasma theory. His next project will be a post-doctoral fellowship at the National Institute of Energy and Materials in Montreal, where he will study laser-plasma interaction.